Countersunk concrete screw (thunderbolt screw) is hardened carbon steel masonry self-tapping anchor. Featured with hi-low thread and chip clearance notches, it cuts thread directly into concrete, brick and block without plastic wall plug. Countersunk head enables flush finish. Torx drive prevents cam-out under high torque. Widely used for window & door frame fixing, timber battens and masonry installation. Sizes M6, M7.5, M8, M10, length range 40–200mm. Zinc plated / Ruspert coating available. Pre-drilling required.